Statically Stable Biped Robotic Mechanism and Method of Actuating

ABSTRACT

A method of actuating a robotic mechanism having a first leg member rotatably coupled to a first side of a chassis and a second leg member rotatably coupled to a second side of the chassis. The method comprises positioning the first leg member and the second leg member generally about 180 degrees with respect to each other and effecting movement of the chassis by rotating both the first leg member and the second leg member with respect to the chassis.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/167,636 entitled “Statically Stable Biped Robotic Mechanism andMethod of Actuating” filed Jul. 3, 2008, which claims the benefit ofU.S. Provisional Application Ser. No. 60/947,948, filed Jul. 4, 2007,entitled “System and method for configuring a locomotion mechanism thatenables a chassis to stand up from a sitting position and to staticallybalance on two legs even with point contacts to the ground and withoutthe need for onboard sensing” as well as U.S. Provisional ApplicationSer. No. 61/037,688, filed Mar. 18, 2008, entitled “Efficient actuationconfiguration for two-legged robot locomotion”, the contents of whichare hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to robotic mechanisms and, moreparticularly, relates to robotic mechanisms having two legs and methodsof actuating.

2. Background Information

Conventional electric-powered biped robots such as humanoid robotsmaintain balance by having large feet and actively controlling theirbody posture. By adjusting the posture, they position their centerdirectly above the foot touching the ground to achieve stability. Thisis made easier with large feet that provide large contact areas with theground. In most embodiments, such robots rely on inertia sensing toactively control the location of the center of gravity and maintain itabove the feet.

Such balancing control strategies provide static stability, i.e. therobot maintains its balance throughout its walking gait. Its movementcan be interrupted at any time without loss of stability. One example isthe zero moment point (ZMP) strategy, commonly used in humanoids.

Conventional biped robots have multiple electric motors installed intheir legs, such as at the hip, knee and ankle. Consecutive segments ofthe leg are typically connected by motor-gear articulations, whichenables motions of these segments one relative to the other. Thecoordinated actuation of these articulations makes the leg describespecific trajectories and generate locomotion gaits.

The limitations of conventional electric-powered biped design are twofolds. First, actively adjusting the posture to achieve static stabilityleads to relatively slow motions that do not mimic biological gaits, andrequires elaborate sensors and computation. Second, motor-geararticulations dissipate considerable energy every time the foot touchesthe ground, because these transmissions do not store and restore energyefficiently. When the foot impacts the ground, energy is lost toinelastic collisions, making it difficult for biped robots to rundynamically.

The present invention addresses both limitations by providingsensor-free static stability without large feet, and enabling dynamicrunning with elastic legs. The robot's body configuration is designedsuch that its center of gravity is permanently below the hips, whichleads to static stability even in the absence of feet. The legs areactuated by a single motor at the hip, making the legs describe completecircles around the hips. The legs are shaped in a spiral to enable therobot to stand up by simple actuation of the hip motors. No sensing isneeded for static stability or standing up.

Dynamic running is made possible by forming the legs out of compliantmaterial. This provides the legs with elastic properties so they canefficiently store and restore energy each time the leg touches theground. This efficient exchange of energy enables the biped robot to rundynamically.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a robotic mechanism isprovided. The robotic mechanism comprises: a chassis having a firstside, an opposite second side and a center of mass; a first leg memberrotatably coupled to the chassis proximate the first side, the first legmember being of generally spiral shape; and a second leg memberrotatably coupled to the chassis proximate the second side, the secondleg member being of generally spiral shape. Wherein a portion of thefirst leg member and a portion of the second leg member are structuredto engage a surface, wherein the portion of the first leg member has acenter of curvature and the portion of the second leg member has acenter of curvature, and wherein the center of mass of the chassis isdisposed below the center of curvature of the first leg member and thecenter of curvature of the second leg member.

The first leg member and the second leg member may rotate generallyabout a common axis and the center of mass of the chassis may bedisposed below the common axis.

The first leg member and the second leg member may be formed from anelastically compliant material. The first leg member may include a firstend and a second end with the first end being rotatably coupled to thechassis. The first leg member may be generally shaped such that thedistance from the first end to a point on the first leg increasesmonotonically as the point describes the leg profile starting from thefirst end and ending at the second end. The distance from the first endto a point on the first leg member may remain constant over a portion ofthe first leg member as the point describes the profile of the portionmoving along the portion from the first end of the first leg membertoward the second end of the first leg member. The distance from thefirst end to a point on the first leg member may monotonically decreaseover a portion of the first leg member as the point describes theprofile of the portion moving along the portion from the first end ofthe first leg member toward the second end of the first leg member.

The second leg member may include a first end and a second end with thefirst end being rotatably coupled to the chassis. The second leg membermay be generally shaped such that the distance from the first end to apoint on the second leg member increases monotonically as the pointdescribes the leg profile starting from the first end and ending at thesecond end. The distance from the first end to a point on the second legmember may remain constant over a portion of the second leg member asthe point describes the profile of the portion moving along the portionfrom the first end of the second leg member toward the second end of thesecond leg member. The distance from the first end to a point on thesecond leg member may monotonically decrease over a portion of thesecond leg member as the point describes the profile of the portionmoving along the portion from the first end of the second leg membertoward the second end of the second leg member.

As another aspect of the invention, a robotic mechanism is provided. Therobotic mechanism comprises: a chassis having a first side and anopposite second side; a first leg member rotatably coupled to thechassis proximate the first side; and a second leg member rotatablycoupled to the chassis proximate the second side. The first leg memberand the second leg member being structured upon rotation to move thechassis from a first position in which the chassis is resting on asurface to a second position in which the chassis is positioned adistance above the surface.

The first leg member may be of generally spiral shape and the second legmember may be of generally spiral shape.

As a further aspect of the invention, a method of actuating a roboticmechanism is provided. The method comprises: rotating a first leg memberwith respect to a chassis, rotating a second leg member with respect tothe chassis, and responsive to rotation of the first leg member androtation of the second leg member, effectuating a movement of thechassis. The first leg member being rotatably coupled to the chassisproximate a first side, the second leg member being rotatably coupled tothe chassis proximate a second side and the first leg member and thesecond leg member being of generally spiral shape and rotate generallyabout a common axis that lies above a center of mass of the chassis.

The first leg member and the second leg member may be rotated at aconstant speed. The first leg member and the second leg member may berotated at a varying speed.

The method may further comprise orienting the first and second legmembers out of phase with respect to each other. The step of orientingmay comprise moving one of the first leg member and the second legmember about 180 degrees out of phase with the other of the first legmember and the second leg member. The step of orienting may comprisemoving both the first leg member and the second leg member such that thefirst leg member and the second leg member are about 180 degrees out ofphase with respect to each other.

The step of rotating the first leg member may comprise rotating at aconstant speed and the step of rotating the second leg member maycomprise rotating the second leg member at a constant speed. The step ofrotating the first leg member may comprise rotating the first leg memberat a varying speed and the step of rotating the second leg member maycomprise rotating the second leg member at a varying speed.

The movement of the chassis may comprise a hopping motion. The movementof the chassis may comprise bipedal locomotion.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the invention can be gained from the followingdescription of the preferred embodiments when read in conjunction withthe accompanying drawings in which:

FIG. 1 is an isometric view of a robotic mechanism in accordance with anembodiment of the invention;

FIG. 2 is a side elevation view of a leg member of the robotic mechanismof FIG. 1;

FIG. 3 is a side view of the robotic mechanism of FIG. 1 showingprogressive movement of the leg members about the chassis; and

FIG. 4 is side view of the robotic mechanism of FIG. 1 showing analternate orientation of the leg members.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Directional phrases used herein, such as, for example, left, right,front, back, top, bottom and derivatives thereof, relate to theorientation of the elements shown in the drawings and are not limitingupon the claims unless expressly recited therein.

As employed herein, the statement that two or more parts are “coupled”together shall mean that the parts are joined together either directlyor joined through one or more intermediate parts.

As employed herein, the term “number” refers to the quantity one or aninteger greater than one (i.e., a plurality).

Referring to FIG. 1, an example robotic mechanism 10 is shown. Therobotic mechanism 10 includes a chassis 12 having a first side 14 and anopposite second side 16. Chassis 12 is preferably formed from a rigidmaterial (e.g., without limitation, aluminum, carbon fiber, wood,plastic) but may also be formed from other suitable materials. In someembodiments, the chassis 12 may be designed to accommodate a decorativeand/or protective shell (not shown) that defines a certain appearancesuch as, without limitation, a robotic animal or a humanoid. Rotatablycoupled to the first side 14 is a first leg member 20. Similarly, asecond leg member 22, is rotatably coupled to the opposite second side16. Preferably, the first leg member 20 and the second leg member 22 arecoupled to the chassis 12 in a manner such that they both independentlyrotate about a common rotational axis 24. However, some embodiments mayhave both legs coupled.

In the example shown in FIG. 1, chassis 12 includes a first motor 30 anda second motor 32. An output shaft (not numbered) of the first motor 30is coupled to the first leg member 20 via a first gear train 34 so as totranslate rotational power from first motor 30 to first leg member 20.Likewise, an output shaft (not numbered) of the second motor 32 iscoupled to the second leg member 22 via a second gear train 36 so as totranslate rotational power from second motor 32 to second leg member 22.It is to be appreciated that although two motors 30, 32 and two geartrains 34, 36 are shown in the example described herein, a single motorcoupled to one or more gear trains could be used to provide independentrotational movement to the first and second leg members 20, 22. Althoughnot shown in the Figures, it is also to be appreciated that chassis 12may further include motor control electronics including, but not limitedto, a positioning device and power drive circuitry, as well as one ormore power sources (e.g., without limitation, batteries). Suchpositioning device or devices are employed to measure, sense or estimatethe position of each of the motors 30,32 or leg members 20,22, or acombination thereof, so that the position of each leg can be measured orestimated directly from measurements. Position estimation, sensing andmeasurement can occur at some or all positions of the legs or motors,and at some or all times during operation.

The position, velocity and/or timing of each leg is preferablycontrolled by feedback control software and electronics that have accessto all leg positions or actuator positions by reading the output of thepositioning device(s). The feedback control software sends independentposition, velocity, acceleration or current commands to each motor andensures tracking of such commands by reading leg position measurements.In some embodiments, additional onboard sensors such as inertia, visionand range finding sensors can be used by the feedback control softwareto control each of the leg members 20,22. The control software isresponsible for positioning each of the leg members 20,22 at specificorientations, rotating each of the leg members 20,22 at specific speeds,and synchronizing the relative position, velocity and timing of each ofthe leg members 20,22.

Control of rotation of each of the leg members 20,22 can also beperformed without feedback control software by directly or indirectlycoupling positioning devices to the motors 30,32, whereby positionssensed, measured or estimated regulate each of the motor's 30,32position, speed of rotation, or acceleration. Control of rotation ofeach of the leg members 20,22 can also be performed without feedbackcontrol software by setting the motor's 30,32 position, speed ofrotation, or acceleration to predefined values without using apositioning device (open-loop control or feed-forward control). As such,it is to be appreciated, as will be described in further detail below,that chassis 12 does not require any positioning devices or othersensing equipment in order to maintain static stability.

Control of rotation of each of the leg members 20,22 can also beperformed without feedback control software by setting the motor's 30,32position, speed of rotation, or acceleration to predefined valueswithout using a positioning device (open-loop control or feed-forwardcontrol).

Referring to FIG. 2, an example leg member 20,22 is shown. In an exampleembodiment of the present invention, such as shown in FIG. 1, both thefirst leg member 20 and the second leg member 22 are of substantiallysimilar, if not identical, shape and construction. Each leg member 20,22is preferably formed out of plastic, fiberglass or other suitablematerial having compliance properties to absorb at least some of theshock energy when a leg member 20,22 contacts the ground surface 40 andto restore some of the absorbed energy when the leg 20,22 leaves theground surface 40. Although less than ideal, it is to be appreciatedthat leg members 20,22 may also be formed from materials lacking suchcompliance properties. Each leg member 20,22 has a first end 26 and asecond end 28 with each leg member 20,22 being rotatably coupled to thechassis 12 at or near the respective first end 26 so as to rotategenerally about the rotational axis 24 previously discussed. Each of theleg members 20,22 are preferably generally spiral shaped such that adistance D from the rotational axis 24, at or near first end 26, to apoint on the leg member 20,22 generally increases monotonically as thepoint describes the profile of the leg member 20,22 starting from thefirst end 26 and ending at the second end 28. Such monotonical increasein the distance D is shown in the example of FIG. 2 in the portion ofthe leg member 20,22 between the first end 26 and point VI, where thedistances shown are related as D<D1<D2<D3<D4<D5 with D being the leastand D5 being the greatest. However, it is to be appreciated that someembodiments, (such as the one shown in the Figures) may includelocalized portions of the leg member 20,22 having non-monotonicallyincreasing distances. In such localized portions, the distance from thefirst end may remain constant or may decrease. An example of suchlocalized portions is shown in the example leg member 20, 22 of FIG. 2,where the distance from the first end 26 to a point on the leg membergenerally decreases moving from points VI to VII and generally remainsconstant moving from point VIII to second end 28.

Referring to FIG. 3, static stability of the robotic mechanism 10,without the need for sensing equipment, is provided by arranging thepreviously described components associated with the chassis (e.g.,without limitation, first and second motors 30,32; first and second geartrains 34,36), relative to the chassis 12 such that the resultant centerof mass CM (i.e., center of gravity) of the chassis 12 and componentslies below the leg's center of curvature CC (shown approximated inpositions b and c of FIG. 3) at the point (or portion) where the legtouches the ground. It is to be appreciated that the center of curvatureof each of the leg members 20,22 varies along the length of the legmembers 20,22 and thus is dependent upon the point (or portion) of theleg member being considered. In a preferred embodiment, the CM also liesvertically below the point of coupling of the first and second legmembers 20,22. In other words, the center of mass of the chassis 12 liesbelow rotational axis 24. Such an arrangement allows for staticstability of the robotic mechanism 10 even with point ground contacts asthe gravitational force acting on the chassis 12 and related componentsis aligned with the reaction force (not shown) acting on each of the legmembers 20,22 at all leg orientations as long as the chassis 12 is notresting on a surface. FIG. 3 shows an example of the leg members 20,22(only second leg member 22 is visible in the side view of FIG. 3) of therobotic mechanism 10 positioned in some example possible orientations inwhich the chassis 12 is not resting on the surface 40 (see positions b,c and d) as well as the leg members 20,22 oriented such that the chassis12 is resting on the surface 40 (see position a). It is to beappreciated that FIG. 3 merely shows leg members 20,22 oriented in someexample positions and that leg members 20,22 rotate completely aboutrotational axis 24 and therefore may be positioned in any orientationrelative to the chassis 12 about axis 24.

Having thus described the basic elements of the robotic mechanism 10, aswell as how static stability is achieved, actuation and movement of therobotic mechanism will now be described. As shown in stages a, b, c andd of FIG. 3, the unique shape of leg members 20,22 allows for therobotic mechanism 10 to move from a position in which the chassis 12 isresting on a surface 40, shown at a, to a position in which chassis 12is elevated above the surface 40 (shown at b, c, and d) by generallysimultaneously rotating generally aligned leg members 20,22 throughabout 180 degrees in the direction of rotation as indicated by arrow R.By generally aligned, it is to be understood that both the first legmember 20 and the second leg member 22 are oriented with respect to thechassis 12 in a generally equivalent manner (same phase). In continuedreference to FIG. 3, it can be appreciated that jumping and hoppingmovements of the robotic mechanism 10 can be achieved by generallysimultaneously actuating the legs in the direction R at high speed whilemaintaining the legs in the same phase. Actuating the legs once (onecomplete rotation) produces jumping, more than once (multiple rotations)produces hopping. Hopping can also be produced by actuating the legsforward and backward repeatedly. During hopping, the chassis 12 does notcontact the surface 40. During hopping, the phase between the first legmember 20 and the second leg member can be varied to induce turningmotion. The term “phase,” as used herein, is to be understood to referto the difference of angular orientation between leg members 20 and 22.

Walking, jogging and running behaviors of the robotic mechanism 10 canbe achieved in two ways. In a first method, the first leg member 20 andthe second leg member 22 are first oriented generally about 180 degreesfrom one another, as shown in FIG. 4, which can be accomplished throughrotation of one or both of the first and second leg members 20,22. Oncethe leg members 20,22 are positioned in such relative orientation, bothleg members 20,22 are then actuated in the direction of motion at thesame constant speed. In some embodiments, leg actuation can be performedwith a single motor driving both leg members 20,22 through a gearingmechanism. It is to be appreciated that by varying the actuation speed,the movement of the robotic mechanism 10 may be varied from walking tojogging to running movements. Additionally, it is to be furtherappreciated that turning motions could readily be accomplished byvarying the actuation speed of one or both of the leg members 20,22(e.g., without limitation, slow only the right leg to turn right, slowonly the left leg to turn left, accelerate the left leg to turn right,accelerate the right leg to turn left, or a combination of slowing oneleg and accelerating the other leg).

In a second method, each of the first and second leg members 20,22 areactuated to rotate around the rotational axis 24 following a timedprofile that specifies the leg angle at each instant of time. The phaseof the timed profile for one of the first and second leg members 20,22is offset from the profile of the other leg by half a period of legrotation in order to generate an alternating biped gait. For example,first leg member 20 may follow a timed profile in which the leg member20 rotates at a first rotational speed while in contact with the groundand at a second, faster rotational speed when not in contact with theground. Similarly the second leg member 22 may follow the same timedprofile except time delayed by half of the time it takes to complete afull revolution. Through variations in magnitudes of the rotationalspeeds, in the time and leg position at which each speed starts andends, and in the duration for the legs to complete one revolution, themotion may be switched from walking, jogging or running. Walking gaitsare generally characterized with at least having one leg touching theground at any time, where as jogging and running are characterized byperiods of time where no leg touches the ground. Additionally, turningbehavior can be achieved by increasing or decreasing the rotation speedof the leg member 20,22 touching the ground relative to the speed of theother leg member 20,22 when it last touched the ground. Turning in placecan be achieved by actuating the leg members 20,22 in oppositedirections, or by actuating only one of leg members 20,22 on the sideopposite of the direction of turn.

In addition to the movements previously described, it is to beappreciated that other movements/actuations could also be carried out bythe robotic mechanism 10. Such other movements/actuations include,without limitation dancing and swimming. A dancing animation may beachieved by moving the leg members 20,22 independently, following twopossibly different timed profiles, one for each leg. A swimming behaviormay be achieved by having a positively buoyant and watertight bodyassociated with the chassis 12 and activating the walking and turningbehaviors previously described while in the water.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the claims appended and any and all equivalents thereof.

1. A method of actuating a robotic mechanism having a first leg memberrotatably coupled to a first side of a chassis and a second leg memberrotatably coupled to a second side of the chassis, the methodcomprising: positioning the first leg member and the second leg membergenerally about 180 degrees with respect to each other; and effectingmovement of the chassis by rotating both the first leg member and thesecond leg member with respect to the chassis.
 2. The method of claim 1wherein positioning the first leg member and the second leg membergenerally about 180 degrees with respect to each other comprises:rotating both the first leg member and the second leg member.
 3. Themethod of claim 1 wherein positioning the first leg member and thesecond leg member generally about 180 degrees with respect to each othercomprises: rotating only one of the first leg member and the second legmember with respect to the other one of the first leg member and thesecond leg member.
 4. The method of claim 1 wherein the first leg memberand the second leg member are rotated at a constant speed.
 5. The methodof claim 1 wherein the first leg member and the second leg member arerotated at different speeds.
 6. The method of claim 1 wherein each ofthe first leg member and the second leg member are each rotatedaccording to a timed profile that specifies the position of each of thefirst leg member and the second leg member at each instant of time. 7.The method of claim 6 wherein the timed profile of the first leg memberdiffers from the timed profile of the second leg member.
 8. A method ofactuating a robotic mechanism, the method comprising: rotating a firstleg member with respect to a chassis; rotating a second leg member withrespect to the chassis; and responsive to the rotation of the first legmember and the rotation of the second leg member, effectuating amovement of the chassis, wherein the first leg member is rotatablycoupled to the chassis proximate a first side and the second leg memberis rotatably coupled to the chassis proximate a second side.
 9. Themethod of claim 8 wherein the first leg member and the second leg memberrotate generally about a common axis that lies above a center of mass ofthe chassis.
 10. The method of claim 8 wherein the first leg member andthe second leg member are rotated at a constant speed.
 11. The method ofclaim 8 wherein the first leg member and the second leg member arerotated at a varying speed.
 12. The method of claim 8 further comprisingorienting the first and second leg members out of phase with respect toeach other.
 13. The method of claim 12 wherein the step of orientingcomprises moving one of the first leg member and the second leg memberabout 180 degrees out of phase with the other of the first leg memberand the second leg member.
 14. The method of claim 12 wherein orientingthe first and second leg members comprises moving both the first legmember and the second leg member such that the first leg member and thesecond leg member are about 180 degrees out of phase with respect toeach other.
 15. The method of claim 12 wherein rotating the first legmember comprises rotating the first leg member at a constant speed andwherein rotating the second leg member comprises rotating the second legmember at a constant speed.
 16. The method of claim 12 wherein rotatingthe first leg member comprises rotating the first leg member at avarying speed and wherein the step of rotating the second leg membercomprises rotating the second leg member at a varying speed.
 17. Themethod of claim 8 wherein the movement comprises a hopping motion. 18.The method of claim 12 wherein the movement comprises bipedallocomotion.
 19. A robotic mechanism comprising: a chassis having a firstside, an opposite second side and a center of mass; a first leg memberrotatably coupled to the chassis proximate the first side; and a secondleg member rotatably coupled to the chassis proximate the second side;wherein a portion of the first leg member and a portion of the secondleg member are structured to engage a surface, and wherein the first legmember and the second leg member are disposed generally about 180degrees with respect to each other about a common rotational axis. 20.The robotic mechanism of claim 19, wherein the first leg member and thesecond leg member rotate generally about a common axis and wherein thecenter of mass of the chassis is disposed below the common axis.